1. Field of the Invention
This invention relates to complexed iodine products, and, more particularly, to water soluble complexes of polyvinylpyrrolidone, hydrogen chloride and iodine, and to a process for preparing such water soluble complexes as a stable, free-flowing powder having substantially all of its complexed iodine available for antibacterial activity.
2. Description of the Prior Art
Iodine has been used as a disinfectant for nearly 150 years; however, its low solubility in water has required formulation in alcohol, known as "tincture of iodine" or with metallic salts such as sodium or potassium iodide, known as Lugol's solution. A water soluble form of iodine then was developed in which iodine was complexed with water soluble polyvinylpyrrolidone (PVP), which is an inert Carrier. The PVP-I.sub.2 complex, however, was not entirely satisfactory. In particular, during preparation of the complex, 1/3 of the iodine reactant was reduced to iodide ion which does not contribute to antimicrobial activity. Thus, the PVP-I.sub.2 complex required 17.2% iodine reactant to produce a 10% active iodine product.
Accordingly, it has been desired to provide a water soluble complex of iodine having an increased available iodine content relative to the amount of iodine used for its preparation. Hosmer, W., in U.S. Pat. No. 2,754,245, issued July 10, 1956, thus provided a water soluble iodine monochloride adduct of polyvinylpyrrolidone by heating a mixture of the compounds. However, the total iodine used was 17.4% while available iodine was only 10.1%
Later, Schenck, H. et al., in an article in Makromol. Chem., 181, 1871-1888 (1980), entitled "Some Model Studies on the Chemistry and Structure of Polyvinylpyrrolidone Halogen Carriers", described a solution process for the preparation of a water-insoluble complex of polyvinylpyrrolidone, hydrogen chloride and iodine. The process comprised mixing a solution of PVP in methanol with aqueous HCl and iodine, and drying the residue in a vacuum desiccator. The water insolubility property of this adduct, however, is disadvantageous for commercial use, where aqueous solutions are preferred formulations.
Schenck, H. et al., in the J. Pharmaceutical Sciences 68, No. 12, 1505-1509 (1979), entitled "Structure of Polyvinylpyrrolidone-Iodine (Povidone-Iodine)", attributed part of the water solubility of PVP-I.sub.2 complexes to the appreciable number of free pyrrolidone moieties in the complex. Free pyrrolidone moieties are units of the PVP polymer which do not participate in complexation of I.sub.2 present in the form of I.sub.3.sup.- ions. More particularly, in the PVP-I.sub.2 complex, 18 units of PVP are free while 2 units of PVP are utilized for complexation. The structure of the complex thus is an adduct of the PVP polymer and hydrogen triiodide in which a proton is fixed by hydrogen bonding between two carbonyl groups of two pyrrolidone rings, either vicinal or non-vicinal, and the triiodide anion is bound ionically to the hydrogen cation, as shown pictorially below: ##STR1##
Apparently, the water-insoluble PVP/HCl/I.sub.2 complex of Schenck did not possess the requisite free PVP units necessary to provide water solubility.
Accordingly, it is an object of this invention to provide a water soluble complex of PVP, HCl and I.sub.2.
Another object herein is to provide a water soluble PVP/HCl/I.sub.2 complex in which substantially all of the iodine therein is available for antimicrobial activity.
Still another object is to provide a water soluble PVP/HCl/I.sub.2 complex which is a stable, non-toxic, free flowing, lightly colored, dry powder having effective antimicrobial activity.
Yet another object herein is to provide aqueous solutions of water soluble PVP/HCl/I.sub.2 complexes which are stable, and skin insensitive, and show antimicrobial activity at iodine levels lower than that of commercial, complexed iodine products.
Another object of the invention is to provide a process for preparing water soluble complexes of PVP, HCl and I.sub.2.
A particular object herein is to provide such a process in which a substantial number of free pyrrolidone units remain intact during preparation of the complex, and substantially all of the iodine reactant is complexed as available iodine.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.